Major, Career? What to do?

I am in a dilemma. I can make decisions on most things in my lift, but I can't make a decision about what I want to do. At first I want to be a doctor, but at the rate I am doing in science classes (Bs and Cs and not As) in college, I am not sure that going to med-school is even possible. Plus, if this is so, then doesn't this means that being a doctor is not the right choice for me? I am not sure what to do. I think I am good at managing things, but should I change my major to management science... If so then I really need to go talk to Career center and at least take some of the classes for management science. I feel that I am running behind in college, and if so, then I might have to take a fifth year, which means that financial aid might not even cover for me. This means that I am under a lot of pressure. Ugh!!!!! I am so frustrated.